Again, the precondition is a LEMP installation as described in this article: Installation of Nginx, MySQL and PHP
Seafile has a its own little web server, but it can not handle the HTTPS protocol. So, to get an encrypted transmission to the cloud, you have to run Seafile behind a "real" web server - in this case, nginx.

Whether you want to run OwnCloud, Baikal or WordPress on the Banana Pi - you will need a web server, MySQL and PHP. I have decided to use Nginx as web server, since it is very resource-friendly compared to Apache. And it is also known for its performance and stability.